Scanning device



Sept. 14, 1954 A. L. LAWRENCE SCANNING DEVICE Filed Sept. 16, 1949INVENTOR ARTHUR L. LAWRENCE [ATTORNEYS Patented Sept. 14, 1954 SCANNINGDEVICE Arthur L. Lawrence, Oyster Bay, N. Y., assignor to FairchildEngine and Airplane Corporation, New York, N. Y., a corporation ofMaryland Application September 16, 1949, Serial No. 116,071

Claims.

This invention relates to scanning devices, and has particular referenceto parabolic scanning reflectors for radar apparatus.

In order to scan the area in front of a radar antenna, it has become thepractice to angularly offset the axis of the reflector from the axis ofthe antenna so that the reflector is tilted, and then rotate theresulting asymmetric reflector at relatively high speed about thestationary antenna. Because of the tilt of the reflector relatively tothe axis of its rotation, the reflector and the corresponding beam tiltcontinuously or wobble about the axis of rotation to cover a materiallylarger scanning area than the crosssectional area of the beam itself.

Although the asymmetric reflector is very effective in affording a largescanning area, the dynamic unbalance caused by the tilt of the rotatingreflector becomes seriousas the speed of rotation of the reflectorincreases, particularly when airborne. Dynamic unbalance is due toforces caused by the eccentric center of mass of the reflector, windageand air density variations, each of which becomes critical at highrotational speeds of the reflector and the resulting vibration may causestructural failure and higher driving power requirements. The expedientof dynamically balancing the reflector by the application of weightscounterbalancing the eccentric center of mass is impractical and mayaggravate the unbalance when the elevation of the device changes inflight.

In accordance with the present invention, an asymmetric radar scanningdevice is provided whose rotating reflector is and remains dynamicallybalanced throughout a very wide range of rotational speeds and underwidely varying windage and air density variations.

In a preferred embodiment of the invention the tilting parabolicreflector is imbedded in solid dielectric material shaped in the form ofa cylinder mounted coaxially with the axis of rotation of the reflectorwhich it encloses. Preferably, the dielectric material is a moldableplastic which becomes porous on setting so as to be light in weight andyet having sufficient strength and rigidity to withstand high rotationalspeeds and to support the metallic reflector so that it may be made oflightweight metal foil, thus making the entire reflector-casingcombination lightweight so as to reduce driving power requirements.

It will be seen that the dynamically-balanced asymmetrical radarscanning device of this invention may be utilized in any desiredenvironment without impairment of its function by reason of change oforientation, elevation, or speed of rotation, these advantages being dueto the smooth symmetrical surface and dynamic balance of the rotatingscanning device, which also enable it to be rotated at very high speedswithout vibration, thereby materially increasing the scanning rate andimproving the signal over noise level ratio.

For a more complete understanding of the invention, reference may be hadto the accompanying drawings, in which:

Figure 1 is an axial cross-section through the scanning device of thisinvention as seen along the line I--l of Fig. 2; and

Fig. 2 is a face view of the new scanning device.

Referring to the drawings, numeral l0 designates a radar antenna whichdoes not rotate, but about whose axis A the parabolic reflector llrotates, but with its focal axis or its axis of revolution B tilted atan angle, say 9, to the axis A of the antenna l0 and its supportingconduit l2 containing the conductors leading to the electronicequipment, not shown.

The parabolic reflector II is carried by the rotating, generallycylindrical unit designated I3,

which includes a dished backing plate [4 of relatively rigid pressedsheet metal, which is secured by screws 15 to the flange of a hub l6journalled in bearing I I mounted in a frame l8, which preferably iscarried in a conventional gimbal suspension, forming no part of thisinvention, but enabling the unit 13 and the antenna Hi to be oriented atany desired angle.

A spur gear [9 is formed on or secured to the flange of the hub l6 andis engaged by a pinion 20 journalled in frame I8 and driven by a shaft2| from an electric motor, also carried by the gimbal suspension, andnot shown. By means of the shaft and gear train l9-20, the unit 13 isrotated about the axis of the antenna It at very high speeds, which aremade possible by this invention, as will be described.

The cylindrical unit I3, including the parabolic reflector H and backingplate I 4 also includes a cylindrical mass of dielectric materialencasing the reflector H and preferably composed of a synthetic resinhavinglightness, strength and hardness, and capable of being machined orotherwise cut to shape. A suitable material is foam Hycar which is abutadiene-acrylonitrile copolymer or a butadiene-styrene copolymer whichhas been expanded into a hard, non-permeable, cellular mass of lowdensity. Another suitable material of similar characteristics isStyrofoam, which is an expanded polystyrene.

The resinous cylinder is preferably formed in two complementarycomponents, 22 and 23, positioned on opposite sides of the reflector ll.The rear or inner component 22 is bonded or otherwise secured to theinner surface of the backing plate M to a substantial thickness with itsexposed surface molded or subsequently machined to conform to theconcave configuration of the rear of the parabolic reflector II, whenits focal axis B is tilted at an angle to the axis of rotation of thebacking plate it which is coaxial with the axis of the antenna A, asindicated in Fig. 1.

Similarly, the second or front component 23 of the initially plasticmaterial is molded,.or shaped by machining, so that its rear surface hasa parabolic convexity about the axis B mating or complementary with theparabolic concavity of the rear component 22. Preferably, the out ersurface of the front component 23 is dished at 24 to avoid excessive orunnecessary weight.

Having formed the components 22 and 23 described, they mate to jointlyform a rigid support for the parabolic reflector H which accordingly maybe metal foil such as aluminum or tin foil, or the like. By making thereflector ll of tinfoil, the reflector l I need not be separately formedbut partakes of the parabolic contour of mating parts 22 and 23 and doesnot add appreciably to the weight of the rotating unit 13. Instead ofmetal foil, a metallic layer may be otherwise applied to the parabolicsurface of component 22 or 23 as by spraying the metal in molten statethereon, or applying it as a paint in which the finely-divided metal isdispersed, or the like. Thereafter, the metal reflector H and the tworespective concave and convex components 22 and 23 are cemented togetherinto the single, cylindrical, rigid unit is which is bored centrally toprovide an aperture through which the stationary antenna conduit [2passes, as shown in Fig. 1.

Alternatively, the parabolic reflector l i may be made of thin butself-sustaining material such as sheet metal pressed to shape betweenparabolic dies and may serve as a form against which the initiallyplastic material forming components 22 and 23 may be cast or molded orotherwise formed, while the reflector is inclined with its focal axis Bdisposed at an angle to the axis A, as described. As another variationof the method of forming the unit i3, a selfsustaining reflector H,properly oriented at the required angle, may be encased within a mass ofthe resinous material while plastic so that the unit 13 is formed in onestep when the resin hardens.

However the cylindrical unit i3 is formed, it is then trued about axis Aby machining and is otherwise adjusted so that it is smooth and its massdistributed uniformly about the axis of rotation A to afford dynamicbalance at all speeds and angles of orientation of axis A.

In operation of the apparatus of this invention, rotation of the tiltedreflector H by driving gearing as, 26 about the axis of rotation Acauses it to wobble asymmetrically. In view of the fact that thesymmetrical encasing cylinder 22, 23 places the asymmetric reflector Iiin dynamic balance, no vibration ensues nor is' the balance changedduring changes in elevation causing a change in air density, as whenmetrical outer surface, very much higher rotational speeds and moreeflicient scanning are possible than has been realized heretoforebecause of excessive vibration at high speeds caused by dynamicunbalance of the rotating parts. Also because of the smooth andsymmetrical outer surface of the rotating unit 13, M, the acousticalnoise level is materially reduced over that of prior scanning devices.

Although the invention is particularly directed to radar scanners withparabolic reflec tors, it has other utility and the term parabolicreflector, as used herein is equally applic'able to conoids,hyperboloids, spheroids, e1- lipsoids, and other surfaces of revolution.

Although a preferred embodiment of the invention has been illustratedand described herein, it is to be understood that the invention is notlimited thereto, but is susceptible to changes in form and detail withinthe scope of the appended claims.

I claim:

1. In a radar scanning device having an antenna and a reflecting surfaceand adapted to be rotated about an axis which is inclined to the axis ofrevolution of its reflecting surface and which is coincident with theaxis of the cooperating antenna, the combination of a con cave metallicreflector, a symmetrical body of dielectric material massed on oppositesurfaces of said reflector and encasing the reflector and having itssymmetrical axis coincident with the axis of rotation of the reflector,whereby the rotating assembly of the asymmetric reflector and thesymmetric body is dynamically balanced about the said axis of rotation,means supporting said body for rotation about said axis of rotation, anddriving means for rotating said body about said axis of rotation.

2. In a radar scanning device having an an tenna and a reflectingsurface and adapted to be rotated about an axis which is inclined to theaxis of revolution of its reflecting surface and which is coincidentwith the axis of the cooperating antenna, the combination of a concavethin sheet metal reflector, a symmetrical body of dielectric materialformed of two mating blocks having respective concave and convexsurfaces coextensively engaging the corre sponding opposite surfaces ofsaid reflector and jointly encasing the reflector and having itssymmetrical axis coincident with the axis of rotation of the reflector,whereby the rotating assembly of the asymmetric reflector and thesymmetric body is dynamically balanced about the rotated about an axiswhich is inclined to the axis of revolution of its reflecting surfaceand which is coincident with the axis of the cooperating' antenna, thecombination of a concave thin sheet metal reflector, a pair of matingblocks of dielectric material having respective concave and convexsurfaces conforming to the contours of the corresponding oppositesurfaces of said reflector, means securing said blocks together withtheir respective convex and 'concave surfaces in coextensive engagementwith the corresponding opposite surfaces of said reflector for encasingthe reflector, the body of material constituting said blocks beingdistributed uniformly about the axis of rotation of the reflector,whereby the rotating assembly of the asymmetric reflector and thesymmetric body of dielectric material is dynamically balanced about thesaid axis of rotation, means supporting said assembly for rotation aboutsaid axis of rotation, and driving means for rotating said assemblyabout said axis of rotation.

4. A radar scanning device comprising a metalfoil parabolic reflectoradapted to be rotated about a relatively flxed axis and having its focalaxis inclined at an angle thereto, and a mass of dielectric materialformed of complementary parts engaging the opposite surfaces of said reflector and jointly encasing said reflector and distributed uniformlyabout the said relatively fixed axis for supporting said reflector, andmeans supporting said mass for rotation about said relatively fixedaxis, whereby the symmetrical mass effects dynamic balance of saidreflector during rotation thereof.

5. A radar scanning device comprising a metallic parabolic reflectoradapted to be rotated about a relatively fixed axis and having its focalaxis inclined at an angle thereto, a mass of dielectric material formedof two mating blocks having respective concave and convex surfacescoextensively engaging the corresponding opposite surfaces of saidreflector and jointly encasing said reflector and distributed uniformlyabout the said relatively fixed axis for effecting dynamic balance ofsaid reflector during rotation thereof, and means supporting said massfor rotation about said axis.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,342,721 Boerner Feb. 29, 1944 2,413,187 McCurdy et a1 Dec.24, 1946 2,492,358 Clark Dec. 27, 1949 2,531,454 Marshall Nov. 28, 1950FOREIGN PATENTS Number Country Date 579,763 Great Britain .Aug. 15, 1946

